In the mobile communication system in LTE (Long Term Evolution), a cell identifier called PCI (Physical Cell Identifier) is allocated to the cell of a base station (eNB: evolved Node B).
Here, description will be started with PCI (see Non-Patent Document 1).
PCIs in LTE include 504 unique physical-layer cell identifiers. The physical-layer cell identities are grouped into 168 unique physical-layer cell identity groups, each group including three unique identifiers. The physical-layer identity is uniquely defined as follows:NIDcell=3NID(1)+NID(2)  [Formula 1]Herein,NID(1)  [Formula 2]
ranges from 0 to 167, corresponding to the physical-layer cell identity group.
Further,NID(2)  [Formula 3]
ranges from 0 to 2, corresponding to the physical-layer cell identity in a certain physical-layer cell identity group.
Herein, three different physical-layer cell identities in the physical-layer cell identity group, i.e.,NID(2)  [Formula 4]
is used as a PSS (Primary Synchronization Signal) code sequence number (e.g., Zadoff-chu sequence used in LTE).
Next, the method of allocating PCI will be described.
The LTE mobile communication system is provided with a database for each base station in which PCIs and the like of the cells of the adjacent base stations in the neighborhood of the concerned base station have been registered. This database is arranged in, for example, a maintenance server.
When PCI is allocated to the target cell of the target base station, a PCI, that has not been allocated as the PCI of any of the cells of adjacent base stations in the neighborhood of the target base station, is allocated to the target cell.
Next description will be made on a cell search that is carried out by the mobile station.
The base station is transmitting, within its own cell, notification signals included with the PCI that has been allocated to the cell, to mobile stations residing in the cell.
The mobile station, based on PSS included in the PCI received from the cell, determines the timing of transmission at which the pilot signal is transmitted from the cell.
Then, the mobile station, in accordance with the determined timing of transmission, receives the pilot signal and measures the reception power of the received pilot signal.
Subsequently, the mobile station searches the cell that has the greatest reception power from among the cells whose reception power has been measured.
Thereafter, the mobile station acquires setup information for connection to the cell, from among the notification signal that is transmitted from the cell thus searched.